A typical wireless communication system includes a number of base stations each radiating to provide coverage in which to serve wireless client devices (WCDs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped devices, whether or not user operated. In turn, each base station may sit as a node on a core network including entities such as a network controller and a gateway system that provides connectivity with an external transport network such as the Internet. With this arrangement, a WCD within coverage of the system may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other WCDs served by the base station.
Such a system may operate in accordance with a particular radio access protocol, examples of which include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) and Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communications (GSM), IEEE 802.11 (WIFI), BLUETOOTH, and others. Each protocol may define its own procedures for registration of WCDs, initiation of communications, handover between base station coverage areas, and other functions.
Further, each base station may provide wireless service to WCDs on one or more carrier frequencies (carriers), each of which could be frequency division duplex (FDD), defining separate frequency channels for downlink and uplink communication, or time division duplex (TDD), defining a frequency channel multiplexed over time between downlink and uplink use. Each carrier or its respective channels could be within a defined frequency band and could be of a particular frequency bandwidth, such as 5 MHz, 10 MHz, or 20 MHz for instance, defining a certain extent of air interface resources.
When a WCD initially enters into coverage of such a base station on a carrier, the WCD may engage in an access process to establish a radio-link layer connection with the base station on that carrier, and the WCD may then engage in an attach process through which the system becomes configured to serve the WCD. In an example attach process, for instance, the WCD may transmit an attach request over the air to the base station, and the base station may forward the attach request to the network controller in the core network. After authenticating and authorizing the WCD, the network controller may then then engage in signaling with the base station and with the gateway system, to coordinate and trigger establishment of a network connection for the WCD. In particular, this process may result in setup of a bearer connection or “bearer” that defines a communication channel extending between the WCD and the gateway system via the base station, including a radio portion extending between the WCD and the base station and an access portion extending between the base station and the gateway system. Further, the process may result in the gateway system or an associated server assigning to the WCD an Internet Protocol (IP) address usable by the WCD to engage in packet-data communication.
Any such bearer established for a WCD may have a corresponding defined service level, which could be indicated by one or more bearer attributes stored in context records at entities along the bearer path, such as at the WCD, the base station, and the gateway system. For example, the service could be indicated by a quality of service class identifier (QCI) and/or corresponding differentiated services point code (DSCP) value, which could be predefined to require handling of communications along the bearer in a particular manner. A high QCI level bearer, such as a bearer with QCIs 1-5 for instance, may be deemed to have a particular guaranteed minimum bit rate, so entities along the bearer path would treat communications on such a bearer as having relatively high priority as compared with other communications, in an effort to satisfy that minimum bit-rate requirement. Further, high QCI level bearer may have other high service level requirements instead or as well. Whereas, a low QCI level bearer, such as a bearer with QCIs 6-9 for instance, may be deemed to be a best-efforts bearer, entitled to whatever best treatment is possible, without a guaranteed minimum bit rate or the like.
Once a WCD is so attached, the base station may then provide the WCD with wireless data communication service. In an example arrangement, for instance, when the WCD has data to transmit on the transport network, the WCD may send a scheduling request over the air to the to the base station, the base station may allocate uplink air interface resources to carry the data over the WCD's radio bearer, the WCD may transmit the data on those allocated resources to the base station, and the base station may forward the data via the WCD's access bearer to the gateway system for output onto the transport network. Likewise, when the gateway system receives data for transmission to the WCD, the gateway system may transmit the data via the WCD's access bearer to the base station, the base station may allocate downlink air interface resources to carry the data over the WCD's radio bearer, and the base station may transmit the data on those allocated resources to the WCD.
In normal operation, when a base station operates in such a wireless network, the base station may thus engage in various types of communication with other network entities. Such communication could be categorized into “control-plane communication” and “user-plane communication”. The control-plane communication encompasses any of the base station's control signaling with other core network entities to help manage operations in the wireless network and service of WCDs, and could thus include communications such as bearer setup signaling, tracking area update signaling, paging, handover signaling, the like. Whereas, the user-plane communication encompasses bearer data being communicated to or from one or more WCDs served by the base station, such as packet data that the base station receives from a gateway system and then schedules/transmits to a WCD and packet data that the base station receives from a WCD and forwards to a gateway system for transmission on a transport network.